Polystyrene-polyacrylate block copolymers, methods of manufacture thereof and articles comprising the same

ABSTRACT

Disclosed herein is a block copolymer comprising a first block derived from a vinyl aromatic monomer; and a second block derived from an acrylate monomer; where a chi parameter that measures interactions between the first block and the second block is greater than or equal to about 0.05, when measured at 240° C. Disclosed herein too is a method comprising polymerizing a vinyl aromatic monomer to form a first block; and polymerizing a second block onto the first block to form a block copolymer; where the second block is derived by polymerizing an acrylate monomer; and where the block copolymer has a chi parameter of greater than or equal to about 0.05, when measured at 240° C.; where the chi parameter is a measure of interactions between the first block and the second block.

This application is a divisional application of U.S. patent applicationSer. No. 13/472,998, filed May 16, 2012, the content of which isincorporated by reference herein in its entirety.

This disclosure is related to polystyrene-polyacrylate block copolymers,methods of manufacture thereof and to articles comprising the same. Inparticular, this disclosure is related to polystyrene-polyacrylate blockcopolymers used for improved nanolithography patterning.

Block copolymers form self-assembled nanostructures in order to reducethe free energy of the system. Nanostructures are those having averagelargest widths or thicknesses of less than 100 nanometers. Thisself-assembly produces periodic structures as a result of the reductionin free energy. The periodic structures can be in the form of domains,lamellae or cylinders. Because of these structures, thin films of blockcopolymers provide spatial chemical contrast at the nanometer-scale and,therefore, they have been used as an alternative low-costnano-patterning material for generating periodic nanoscale structures.While these block copolymer films can provide contrast at the nanometerscale, it is however often very difficult to produce copolymer filmsthat can display periodicity at less than 20 nanometers. Modernelectronic devices often utilize structures that have a periodicity ofless than 20 nanometers and it is therefore desirable to producecopolymers that can easily display structures that have average largestwidths or thicknesses of less than 20 nanometers, while at the same timedisplaying a periodicity of less than 20 nanometers.

Many attempts have been made to develop copolymers that have averagelargest widths or thicknesses of less than 20 nanometers, while at thesame time displaying a periodicity of less than 20 nanometers. Thefollowing discussion details some of the attempts that have been made toaccomplish this.

FIGS. 1A and 1B depict examples of lamella forming block copolymers thatare disposed upon a substrate. The block copolymer comprises a block Aand a block B that are reactively bonded to each other and that areimmiscible with each other. The alignment of lamellae domains can beeither parallel (FIG. 1A) or perpendicular (FIG. 1B) to the surface foredesirable to produce copolymers that can easily display structures thathave average largest widths or thicknesses of less than 20 nanometers,while at the same time displaying a periodicity of less than 20nanometers.

Many attempts have been made to develop copolymers that have averagelargest widths or thicknesses of less than 20 nanometers, while at thesame time displaying a periodicity of less than 20 nanometers. Thefollowing discussion details some of the attempts that have been made toaccomplish this.

FIGS. 1A and 1B depict examples of lamella forming block copolymers thatare disposed upon a substrate. The block copolymer comprises a block Aand a block B that are reactively bonded to each other and that areimmiscible with each other. The alignment of lamellae domains can beeither parallel (FIG. 1A) or perpendicular (FIG. 1B) to the surface of asubstrate surface upon which they are disposed. The perpendicularlyoriented lamellae provide nanoscale line patterns, while there is nosurface pattern created by parallel oriented lamellae.

Where lamellae form parallel to the plane of the substrate, one lamellarphase forms a first layer at the surface of the substrate (in the x-yplane of the substrate), and another lamellar phase forms an overlyingparallel layer on the first layer, so that no lateral patterns ofmicrodomains and no lateral chemical contrast form when viewing the filmalong the perpendicular (z) axis. When lamellae form perpendicular tothe surface, the perpendicularly oriented lamellae provide nanoscaleline patterns. Therefore, to form a useful pattern, control of theorientation of the self-assembled microdomains in the block copolymer isdesirable.

The block copolymer is annealed with heat (in the presence of anoptional solvent), which allows for microphase separation of the polymerblocks A and B at a temperature above the glass transition temperatureand below the order to disorder transition temperature. The annealedfilm can then be further developed by a suitable method such asimmersion in a solvent/developer or by reactive ion etching whichpreferentially removes one polymer block and not the other to reveal apattern that is commensurate with the positioning of one of the blocksin the copolymer. While this method generates self-assembled films witha uniform spacing, it has not proved useful in continuously anduniformly generating self-assembled films having domain sizes of lessthan 20 nanometers with a periodicity of less than 20 nanometers.

Disclosed herein is a block copolymer comprising a first block derivedfrom a vinyl aromatic monomer; and a second block derived from anacrylate monomer; where a chi parameter that measures interactionsbetween the first block and the second block is greater than or equal toabout 0.05, when measured at 240° C.

Disclosed herein too is a method comprising polymerizing a vinylaromatic monomer to form a first block; and polymerizing a second blockonto the first block to form a block copolymer; where the second blockis derived by polymerizing an acrylate monomer; and where the blockcopolymer has a chi parameter of greater than or equal to about 0.05,when measured at 240° C.; where the chi parameter is a measure ofinteraction between the first block and the second block.

FIG. 1A depicts an example of lamella forming block copolymers that aredisposed upon a substrate;

FIG. 1B also depicts an example of lamella forming block copolymers thatare disposed upon a substrate;

FIG. 2 is a graph depicting thermal decomposition data obtained usingthermogravimetric analysis (TGA);

FIG. 3 is a graph depicting differential scanning calorimetry (DSC)thermograms for all of the compositions shown in the Table 1; and

FIG. 4 is a graph depicting small angle xray scattering data (SAXS) forall of the compositions shown in the Table 1.

As used herein, “phase-separate” refers to the propensity of the blocksof block copolymers to form discrete microphase-separated domains, alsoreferred to as “microdomains” or “nanodomains” and also simply as“domains”. The blocks of the same monomer aggregate to form periodicdomains, and the spacing and morphology of domains depends on theinteraction, size, and volume fraction among different blocks in theblock copolymer. Domains of block copolymers can form duringapplication, such as during a spin-casting step, during a heating step,or can be tuned by an annealing step. “Heating”, also referred to hereinas “baking”, is a general process wherein the temperature of thesubstrate and coated layers thereon is raised above ambient temperature.“Annealing” can include thermal annealing, thermal gradient annealing,solvent vapor annealing, or other annealing methods. Thermal annealing,sometimes referred to as “thermal curing” can be a specific bakingprocess for fixing patterns and removing defects in the layer of theblock copolymer assembly, and generally involves heating at elevatedtemperature (e.g., 150° C. to 350° C.), for a prolonged period of time(e.g., several minutes to several days) at or near the end of thefilm-forming process. Annealing, when performed, is used to reduce orremove defects in the layer (referred to as a “film” hereinafter) ofmicrophase-separated domains.

The self-assembling layer comprising a block copolymer having at least afirst block and a second block that forms domains through phaseseparation that orient perpendicular to the substrate upon annealing.“Domain”, as used herein, means a compact crystalline, semi-crystalline,or amorphous region formed by corresponding blocks of the blockcopolymer, where these regions may be lamellar or cylindrical and areformed orthogonal or perpendicular to the plane of the surface of thesubstrate and/or to the plane of a surface modification layer disposedon the substrate. In an embodiment, the domains may have an averagelargest dimension of about 1 to about 25 nanometers (nm), specificallyabout 5 to about 22 nm, and still more specifically about 5 to about 20nm.

The term “M_(N)” used herein and in the appended claims in reference toa block copolymer of the present invention is the number averagemolecular weight of the block copolymer (in g/mol) determined accordingto the method used herein in the Examples.

The term “MW” used herein and in the appended claims in reference to ablock copolymer of the present invention is the weight average molecularweight of the block copolymer (in g/mol) determined according to themethod used herein in the Examples.

The term “PDI” or “

” used herein and in the appended claims in reference to a blockcopolymer of the present invention is the polydispersity (also calledpolydispersity index or simply “dispersity”) of the block copolymerdetermined according to the following equation:

${P\; D\; I} = {\frac{M_{W}}{M_{N}}.}$

As used herein, PtBS-b-PMMA denotes block copolymers ofpoly(4-tert-butylstyrene) and polymethylmethacrylate. As used herein,PS-b-PMMA denotes block copolymers of polystyrene andpolymethylmethacrylate.

The transition term “comprising” is inclusive of the transition terms“consisting of” and “consisting essentially of”.

The term “and/or” is used herein to mean both “and” as well as “or”. Forexample, “A and/or B” is construed to mean A, B or A and B.

Disclosed herein is a block copolymer comprising a first block polymer(hereinafter “first block” or “first block of the copolymer”) and asecond block polymer (hereinafter “second block” or “second block of thecopolymer”) in which the first and second block are chemicallydissimilar and are characterized by an energetic penalty of dissolvingone block into the other block. This energetic penalty is characterizedby the Flory-Huggins interaction parameter or “chi” (denoted by χ) andis an important factor in determining microphase segregation behavior inblock copolymers. Accordingly, the χ value of a block copolymer definesa tendency of the block copolymer to segregate into microdomains as afunction of the block copolymer's weight, chain length, and/or degree ofpolymerization. The chi parameter can often be approximated from thesquare of the difference in Hildebrand solubility parameters of therespective polymers of the block copolymer. In an exemplary embodiment,the chi parameter has a value of greater than or equal to about 0.1 at240° C.

As used herein, the χ parameter denotes the segment-segment interactionparameter associated with a segment volume of 0.118 cubic nanometers(nm³). The molecular weight of a segment, m_(o), in units of g/mol isequal to the segment volume multiplied by the polymer density anddivided by Avogadro's number. Also as used herein, the degree ofpolymerization, N, is defined as the number of segments per blockcopolymer molecule and M_(N)=N×m_(o).

A greater chi parameter between the first block of the copolymer withrespect to the second block of the copolymer promotes the formation ofsmaller, highly periodic lamellar and/or cylindrical domains, which canbe used to produce periodic structures in a substrate upon which thecopolymer is disposed. In an exemplary embodiment, the periodicstructures in the substrate are produced via nanolithography. In oneembodiment, the first block of the copolymer is a block derived from avinyl aromatic monomer while the second block of the copolymer isderived from an ethylenically unsaturated monomer. In one exemplaryembodiment, the vinyl aromatic monomer is an alkylstyrene monomer, whilethe ethylenically unsaturated monomer is an alkyl methacrylate monomer.In another exemplary embodiment, the alkylstyrene monomer is4-tert-butyl styrene, while the alkyl acrylate monomer is methylmethacrylate. In an exemplary embodiment, the first block of thecopolymer is a poly(4-tert-butyl styrene), while the second block of thecopolymer is polymethylmethacrylate. In one embodiment, the first blockof the copolymer may contain a percentage (about 1 to about 50 molepercent) of polystyrenes other than poly(4-tert-butyl styrene), whilethe second block of the copolymer may contain a percentage (about 1 toabout 50 mole percent) of polymethacrylates other thanpolymethylmethacrylate.

The first block of the copolymer and the second block of the copolymerboth have a narrow polydispersity index and as a result form blockcopolymers that display a high degree of periodicity. The copolymershave lamellar and/or cylindrical morphologies and can alignperpendicular to the surface of a substrate upon which they aredisposed, thus making them useful for advanced semiconductor patterning.These block copolymers can be used for creating features on a substrate(upon which they are disposed) that are less than or equal to about 25nanometers. The block copolymer can be further treated via annealing toself-assemble into morphologies that display improved long range orderwhen compared with a comparative copolymer that has the same compositionbut is not annealed. This feature advantageously permits theblock-copolymer to be used as a photoresist with variable interdomainspacings for different lithographic applications.

Disclosed herein too is a method for manufacturing the block copolymer.The method involves using controlled or living polymerization tosynthesize the first block of the copolymer and the second block of thecopolymer that have a narrow polydispersity index. The block copolymercan be manufactured by a number of different methods listed below.

In one exemplary embodiment, the block copolymer is manufactured using asequential anionic polymerization technique where the first monomer isfirst anionically polymerized to form the first block. When the firstblock of the copolymer reaches a desired molecular weight, an endcappingagent is used to attenuate the reactivity of the polymeryl anion of thefirst block, after which the polymerization of the second block isinitiated to form the block copolymer having a desired polydispersityindex.

In another exemplary embodiment, the first block of the copolymer andthe second block of the copolymer are polymerized separately and thenchemically linked together via a covalent bond. In this method, thefirst block of the copolymer and the second block of the copolymer canbe synthesized using different polymerization methods. In yet anotherembodiment, the block copolymer may be manufactured by sequentialmonomer addition using a controlled free radical polymerizationtechnique. The sequential monomer addition strategies can be combinedwith controlled free radical techniques, including atom transfer radicalpolymerization (ATRP), reversible addition fragmentation chain transferpolymerization (RAFT), and other controlled polymerization methods. Inshort, the block copolymers can also be prepared by synthesis of therespective polymers (i.e., the first block of the copolymer and thesecond block of the copolymer) containing complementary chain-endfunctionalities and subsequently reacting these to form the blockcopolymers.

The block copolymer can be a multiblock copolymer. In one embodiment,the multiblocks can include diblocks, triblock, tetrablocks, and so on.The blocks can be part of a linear copolymer, a branched copolymer wherethe branches are grafted onto a backbone (these copolymers are alsosometimes called “comb copolymers”), a star copolymer, or the like. Inan exemplary embodiment, the block copolymer is a linear diblockcopolymer.

The first block of the copolymer is a block derived from a vinylaromatic monomer. The vinyl aromatic monomers that can be polymerized toproduce the first block of the copolymer of the block copolymer arealkylstyrenes. Examples of suitable alkylstyrenes are o-methylstyrene,p-methylstyrene, m-methylstyrene, α-methylstyrene, o-ethylstyrene,m-ethylstyrene, p-ethylstyrene, α-methyl-p-methylstyrene,2,4-dimethylstyrene, monochlorostyrene, p-tert-butylstyrene,4-tert-butylstyrene, or the like, or a combination comprising at leastone of the foregoing alkylstyrene monomers. An exemplary alkylstyrenemonomer is 4-tert-butylstyrene. An exemplary first block of thecopolymer is poly(4-tertbutyl styrene). In one embodiment, the firstblock of the copolymer may contain about 2 to about 10 weight percentvinyl aromatic species that are not derived from 4-tert-butylstyrene.

The weight average molecular weight (M_(w)) of the first block is about2 kg/mol to about 200 kg/mol, specifically about 5 kg/mol to about 100kg/mol and more specifically about 7 kg/mol to about 50 kg/mol grams permole as measured by multi-angle laser light scattering (MALLS) gelpermeation chromatography (GPC) instrument using THF as the mobile phaseat a flow of 1 milliliter per minute (mL/min).

The polydispersity index of the first block is less than or equal toabout 1.20, specifically less than or equal to about 1.10 andspecifically less than or equal to about 1.08 when determined by sizeexclusion chromatography (SEC) with chloroform as the mobile phase (at35° C. and a flow rate of 1 mL/min).

The first block comprises about 20 to about 80 volume percent,specifically about 40 to about 60 volume percent, and more specificallyabout 45 to about 55 volume percent of the total volume of thecopolymer. In an exemplary embodiment, the first block comprises about50 volume percent of the total volume of the copolymer.

The second block of the copolymer is a block derived from an acrylatemonomer. In one embodiment, the first repeat unit (i.e., the acrylatemonomer) has a structure derived from a monomer represented by formula(1):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms.Examples of the first repeat monomer are acrylates and alkyl acrylatessuch as α-alkyl acrylates, methacrylates, ethacrylates, propylacrylates, or the like, or a combination comprising at least one of theforegoing acrylates.

In one embodiment, the first repeat unit has a structure derived from amonomer having a structure represented by the formula (2):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms andR₂ is a C₁₋₁₀ alkyl, a C₃₋₁₀ cycloalkyl, or a C₇₋₁₀ aralkyl group.Examples of the alkyl(α-alkyl)acrylates are methacrylate, ethacrylate,propyl acrylate, methyl methacrylate, methyl ethylacrylate, methylpropylacrylate, ethyl ethylacrylate, methyl arylacrylate, or the like,or a combination comprising at least one of the foregoing acrylates. Theterm “(α-alkyl)acrylate” implies that either an acrylate or(α-alkyl)acrylate is contemplated unless otherwise specified.

As noted above, the second repeat unit is derived from a monomer thathas at least one fluorine atom substituent and has a structurerepresented by the formula (3):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms andR₃ is a C₂₋₁₀ fluoroalkyl group. Examples of compounds having thestructure of formula (3) are trifluoroethyl methacrylate, anddodecafluoroheptylmethacrylate. An exemplary monomer for the secondblock of the copolymer is methyl methacrylate. An exemplary second blockof the copolymer is polymethylmethacrylate. It is to be noted that thesecond block of the copolymer may contain about 2 to about 5 weightpercent acrylate species that are not derived from methylmethacrylate.

The weight average molecular weight (M_(w)) of the second block is about2 kg/mol to about 200 kg/mol, specifically about 5 kg/mol to about 100kg/mol and more specifically about 7 kg/mol to about 50 kg/mol grams permole as measured by multi-angle laser light scattering (MALLS) gelpermeation chromatography (GPC) instrument using THF as the mobile phaseat a flow of 1 milliliter per minute (mL/min). The polydispersity indexof the second block is less than or equal to about 1.20, specificallyless than or equal to about 1.15 and specifically less than or equal toabout 1.10 when determined by size exclusion chromatography (SEC) withchloroform as the mobile phase (at 35° C. and a flow rate of 1 mL/min).The polydispersity index is used to determine the number averagemolecular weight of the respective blocks or of the entire blockcopolymer as desired. In order to convert a weight average molecularweight to a number average molecular weight, the weight averagemolecular weight as measured by gel permeation chromatography (GPC)instrument using THF as the mobile phase at a flow of 1 milliliter perminute (mL/min) is divided by the polydispersity index as determined bysize exclusion chromatography (SEC) with chloroform as the mobile phase(at 35° C. and a flow rate of 1 mL/min).

The second block comprises about 20 to about 80 volume percent,specifically about 40 to about 60 volume percent, and more specificallyabout 45 to about 55 volume percent of the total volume of thecopolymer. In an exemplary embodiment, the second block comprises about50 volume percent of the total volume of the copolymer.

The polydispersity index of the block copolymer is less than or equal toabout 1.20, specifically less than or equal to about 1.15 andspecifically less than or equal to about 1.10 when determined by sizeexclusion chromatography (SEC) with chloroform as the mobile phase (at35° C. and a flow rate of 1 mL/min).

The weight average molecular weight of the block copolymer is about 3 toabout 150, specifically about 7.5 to about 120, specifically about 10 toabout 100, and more specifically about 15 to about 70 kilograms per moleas determined using multi-angle laser light scattering gel permeationchromatography and the polydispersity index. In an exemplary embodiment,it is desirable for the block copolymer to have a weight averagemolecular weight of about 3 to about 120 kilograms per mole.

The block copolymer has an interdomain spacing as measured by smallangle xray scattering of less than or equal to about 40 nanometers,specifically less than or equal to about 32 nanometers, morespecifically less than or equal to about 25 nanometers, and morespecifically less than or equal to about 20 nanometers.

The block copolymer can be manufactured in a batch process or in acontinuous process. The batch process or the continuous process caninvolve a single or multiple reactors, single or multiple solvent andsingle or multiple catalysts (also termed initiators). In oneembodiment, in one method of manufacturing the block copolymer, a firstmonomer is polymerized anionically to form the first block of thecopolymer in a first reactor in the presence of a first solvent and afirst initiator. A first endcapping agent is then introduced into thefirst reactor to quench the anionic reaction in the first reactor and toprevent undesirable side reactions. The second monomer is anionicallypolymerized into the second block of the copolymer in the presence of asecond solvent and a second initiator. The second block may bepolymerized in a second reactor. When the second block has reached adesirable molecular weight, the reaction may be quenched using a secondendcapping agent. The first block and the second block are thencovalently bonded to form the block copolymer. In one embodiment, thefirst block and the second block are then copolymerized (i.e.,chemically (covalently) bonded) to form the block copolymer in the firstreactor or the second reactor. The first reactor, the first solvent andthe first initiator can be the same or different from the secondreactor, the second solvent and the second initiator.

In an exemplary embodiment, the first reactor is the same as the secondreactor, the first solvent is the same as the second solvent and thefirst initiator is the same as the second initiator. In one embodiment,the first monomer is polymerized anionically to form the first block ofthe copolymer in the first reactor in the presence of the first solventand the first initiator. A first end reactivity attenuating agent isthen introduced into the first reactor to reduce the reactivity of theanion reaction in the first reactor and to prevent undesirable sidereactions. In another embodiment, a reactivity accelerating agent may beintroduced into the first reactor to increase the rate of the anionicreaction in the first reactor.

In one embodiment, the reactivity attenuating agent or the reactivityaccelerating agent is added to the reactor to control the rate of thereaction (of the first block) to a value that is approximate to that ofthe rate of reaction for the second block.

The second monomer is then introduced into the first reactor and isanionically polymerized to form the second block that results in theformation of the block copolymer. The anionic polymerization to form thesecond block is conducted in the presence of the first solvent and thefirst initiator. In one exemplary embodiment, no additional firstinitiator is added to the first reactor. This method of copolymerizationis termed sequential polymerization. An end capping agent is thenintroduced into the first reactor to end-cap the copolymer.

Suitable solvents for conducting the reaction are polar solvents,non-polar solvents, or combinations thereof. Examples of solvents areaprotic polar solvents, polar protic solvents, or non polar solvents. Inone embodiments, aprotic polar solvents such as propylene carbonate,ethylene carbonate, butyrolactone, acetonitrile, benzonitrile,nitromethane, nitrobenzene, sulfolane, dimethylformamide,N-methylpyrrolidone, or the like, or combinations comprising at leastone of the foregoing solvents may be used. In another embodiment, polarprotic solvents such as water, methanol, acetonitrile, nitromethane,ethanol, propanol, isopropanol, butanol, or the like, or combinationscomprising at least one of the foregoing polar protic solvents may alsobe used. Other non-polar solvents such a benzene, alkylbenzenes (such astoluene or xylene), methylene chloride, carbon tetrachloride, hexane,diethyl ether, tetrahydrofuran, or the like, or combinations comprisingat least one of the foregoing solvents may also be used. Co-solventscomprising at least one aprotic polar solvent and at least one non-polarsolvent may also be utilized to modify the swelling power of the solventand thereby adjust the rate of reaction. In an exemplary embodiment, thefirst solvent is tetrahydrofuran.

The weight ratio of the solvent to the first monomer is about 5:1 toabout 20:1, specifically about 7:1 to about 15:1, and more specificallyabout 8:1 to about 12:1.

In order to initiate polymerization of the first monomer to form thefirst block of the copolymer, it is desirable to use a first initiatorthat can initiate anionic polymerization of a vinyl aromatic compound.The first initiator is an aliphatic hydrocarbon alkali metal compound,an aromatic hydrocarbon alkali metal compound, an organic aminoalkalimetal compound, or the like, or a combination comprising at least one ofthe foregoing first initiators.

Examples of the alkali metals include lithium, sodium, potassium, or thelike, or a combination comprising at least one of the foregoing alkalimetals. In an exemplary embodiment, the organic alkali metal compoundsinclude an aliphatic and/or aromatic hydrocarbon lithium compoundcomprising 1 to about 20 carbon atoms, a compound comprising one lithiumatom in a single molecule or dilithium, trilithium and tetralithiumcompounds comprising a plurality of lithium atoms in a single molecule.

In an exemplary embodiment, the first initiator is n-propyllithium,n-butyllithium, sec-butyllithium, tert-butyllithium,hexamethylenedilithium, butadienyldilithium, isoprenyldilithium, areaction product of diisopropenylbenzene and sec-butyllithium, areaction product of divinylbenzene, sec-butyllithium and a small amountof 1,3-butadiene, or the like, or a combination comprising at least oneof the foregoing first initiators. An exemplary first initiator issec-butyllithium.

In one embodiment, the first initiator is used in an amount of about 20to about 2000 moles per mole of the first monomer. In an exemplaryembodiment, the first initiator is used in an amount of about 70 toabout 300 moles per mole of the first monomer.

The first monomer is reacted to form the first block of the copolymer ata temperature of about −100° C. to about 150° C., specifically about−80° C. to about 100° C. Reaction temperature is selected for thepolymerization chemistry in order to minimize side reactions and providepolymer with narrow dispersity. This reaction may be conducted under avacuum or at an elevated pressure. In one embodiment, the pressure inthe reaction vessel is about 0.05 to about 10 kilograms per squarecentimeter, specifically about 0.07 to about 2 kilograms per squarecentimeter. The pressure may be applied by using a pressurized inert gassuch as nitrogen, argon, carbon dioxide or the like to the reactor.

In order to initiate polymerization of the second monomer to form theblock copolymer, it is desirable to add the second monomer to thepreformed polymeryl alkali metal compound of the vinyl aromaticcompound. In one embodiment, the second monomer is used in an amount ofabout 20 to about 2000 moles per mole of the initiator. In an exemplaryembodiment, the second monomer is used in an amount of about 70 to about300 moles per mole of the initiator.

In one embodiment, the reaction to form the second block of thecopolymer is conducted at a temperature of about −100° C. to about 150°C., specifically about −85° C. to about 100° C. This reaction may beconducted under a vacuum or at an elevated pressure. In one embodiment,the pressure in the reaction vessel is about 0.05 to about 10 kilogramsper square centimeter, specifically about 0.07 to about 2 kilograms persquare centimeter. The pressure may be applied by using a pressurizedinert gas such as nitrogen, argon, carbon dioxide or the like to thereactor. The reaction may also be conducted under a vacuum if desired.

In order to initiate polymerization of the second monomer to form thesecond block polymer, it is desirable to use a second initiator that caninitiate anionic polymerization of a vinyl aromatic compound. The secondinitiator is optional, i.e., the first initiator may be used topolymerize both the first and the second block of the block copolymer.Examples of suitable initiators are organic alkali metal compounds ofalkali metals such as lithium, sodium, potassium, rubidium, cesium, orfrancium. In one embodiment, the organic alkaline earth metal compoundsare organometallic compounds of alkaline earth metals such as beryllium,magnesium, calcium, strontium, barium, or radium.

Examples of the second initiator are n-butyllithium, sec-butyllithium,tert-butyllithium, 1,1-diphenylhexyllithium, diphenylmethyllithium,1,1-diphenyl-3-methylpentyllithium, fluorenyllithium,triphenylmethyllithium, α-lithiumethyl isobutyrate, oligostyryllithium,polystyryllithium, oligo-α-methylstyryllithium,poly-α-methylstyryllithium, oligobutadienyllithium,polybutadienyllithium, oligoisoprenyllithium, polyisoprenyllithium, andother monovalent organic lithium compounds; diphenylmethylpotassium,triphenylmethylpotassium, diphenylmethylsodium, triphenylmethylsodium,phenylmagnesium bromide, phenylmagnesium chloride, t-butylmagnesiumbromide, t-butylmagnesium chloride, or the like, or a combinationcomprising at least one of the foregoing second initiators. An exemplarysecond initiator is 1,1-diphenylhexyllithium.

In one embodiment, the second initiator is used in an amount of about 0to about 2000 moles per mole of the first monomer. In an exemplaryembodiment, the second initiator is used in an amount of about 70 toabout 300 moles per mole of the first monomer.

As noted above, after polymerization of the first block of thecopolymer, it may be desirable to add a reactivity attenuating agentbefore adding the second monomer to prevent undesirable side reactions.A reactivity attenuating agent is then added to the reactor to modifythe reactivity of the polymeryl alkali metal compound. An exemplaryreactivity attenuating agent is 1,1-diphenylethylene. The reactivityattenuating agent is added to the reactor in an amount of about 1 toabout 10 moles per mole of the initiator. In an exemplary embodiment,the reactivity attenuating agent is used in an amount of about 1.2 toabout 1.5 moles per mole of the initiator. Additives, including metalsalts such as LiCl, can also be added to improve the polydispersity ofthe polymer.

In one embodiment, it is it is desirable to quench the reaction when thesecond block of the copolymer has reached a desired molecular weight.The quenching is accomplished by addition of a protic compound. In apreferred embodiment, the quenching agent is degassed methanol. Thequenching agent is added to the reactor in an amount of about 25 toabout 1,000,000 moles per mole of the initiator. In an exemplaryembodiment, the first endcapping agent is used in an amount of about 500to about 20,000 moles per mole of the copolymer.

In one embodiment, the respective block polymers may be purified by avariety of methods prior to be reacted to form the block copolymer.Purification of the respective block polymers is optional. In anotherembodiment, the reactants, the respective block polymers, and the blockcopolymer may be purified prior to and after the reaction. Purificationmay include washing, filtration, precipitation, decantation,centrifugation, distillation, or the like, or a combination comprisingat least one of the foregoing methods of purification.

In one exemplary embodiment, all reactants including the solvents,initiators and endcapping agents are purified prior to the reaction. Itis generally desirable to use reactants, solvents and initiators thatare purified to an amount of greater than or equal to about 99 wt %purity, specifically greater than or equal to about 99.5 wt % purity andmore specifically greater than about or equal to about 99.9 wt % purity.In another exemplary embodiment, after sequential polymerization of theblock copolymer, the block copolymer may be subjected to purification bymethods that include washing, filtration, precipitation, decantation,centrifugation or distillation. Purification to remove substantially allmetallic impurities and metallic catalyst impurities may also beconducted. The reduction of impurities reduces ordering defects when theblock copolymers are annealed.

In one embodiment, the block copolymer can contain anti-oxidants,anti-ozonants, mold release agents, thermal stabilizers, levelers,viscosity modifying agents, free-radical quenching agents, otherpolymers or copolymers such as impact modifiers, or the like.

The block copolymer after purification may be dissolved in a solvent andthen disposed upon the surface of a substrate to form a block copolymerfilm whose blocks are perpendicular in orientation to the surface of thesubstrate. In one embodiment, the surface of the substrate may contain asurface modification layer disposed thereon prior to the disposing ofthe block copolymer onto the surface of the substrate. The surfacemodification layer can be a block copolymer, a random copolymer, of ablend of homopolymers and form brushes on the surface of the substrate.The substrate can also be patterned such that some areas result inperpendicular orientation while others induce a parallel orientation ofthe block copolymer domains. The substrate can also be patterned suchthat some regions selectively interact, or pin, a domain of the blockcopolymer to induce order and registration of the block copolymermorphology. The substrate can also have topography that induces thealignment and registration of one or more of the domains of the blockcopolymer. The block copolymer of the invention after being disposedupon the substrate is optionally heated to a temperature of up to 350°C. for up to 4 hours to both remove solvent and form the domains in anannealing process. The annealing of the block copolymer can be used tovary the interdomain spacing (i.e., the periodicity) of the cylindricaland/or lamellar domains. The size of the domains can also be varied byannealing.

The domains of the block copolymer form perpendicular to the substrateand the first block aligns to the pattern created on the first domain tothe “pinning” feature on the substrate, and the second block forms asecond domain on the substrate aligned adjacent to the first domain.Where the patterned substrate forms a sparse pattern, and hence thesurface modification layer regions are spaced at an interval greaterthan an interval spacing of the first and second domains, additionalfirst and second domains form on the surface modification layer to fillthe interval spacing of the sparse pattern. The additional firstdomains, without a pinning region to align to, instead alignperpendicular to the previously formed perpendicular orientationinducing surface modification layer, and additional second domains alignto the additional first domains.

One of the domains of the block copolymer (formed from either the firstblock of the copolymer or the second block of the copolymer) may then bepreferentially etched away. A relief pattern is then formed by removingeither the first or second domain to expose an underlying portion of thesurface modification layer. In an embodiment, removing is accomplishedby a wet etch method, developing, or a dry etch method using a plasmasuch as an oxygen plasma. The block copolymer with at least one domainremoved is then used as a template to decorate or manufacture othersurfaces that may be used in fields such as electronics, semiconductors,and the like.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLE 1

This example was conducted to demonstrate a method of manufacturing theblock copolymer. The polymer manufactured herein is anionicallypolymerized. A series of symmetric poly(4-tert-butylstyrene-block-methylmethacrylate) (PtBS-b-PMMA) diblock copolymers with varying molar massand narrow molar mass distribution were prepared using sequentialanionic polymerization. Order-to-disorder transition (ODT) temperatureswere determined as a function of the overall degree of polymerization,N, using a combination of low frequency dynamic mechanical spectroscopy(DMS) and variable temperature small-angle x-ray scattering (SAXS),leading to a mean-field expression for the segment-segment interactionparameter, χ=(41.2±0.9)/T−(0.044±0.002). This material is characterizedby a larger value of χ, and much greater temperature sensitivity, thanpolystyrene-b-PMMA, providing access to tunable lamellar periods (pitch)down to 14 nanometers (nm) at temperatures that can be easily reached.

4-tert-butylstyrene (tBS) (93%), methyl methacrylate (MMA) (>98.5%),1,1-diphenylethylene (DPE) (97%), anhydrous methanol, sec-butyllithium(s-BuLi) (1.4 molar (M)) in hexane), dibutyl magnesium (DBMg) (1 M inheptane), n-butyllithium (n-BuLi) (2.5 M in hexanes), trioctylaluminum(TOA) (25 wt % in hexanes), and calcium hydride powder were purchasedfrom Sigma-Aldrich. Deuterated chloroform (CDCl₃) was purchased fromCambridge Isotope Labs. Tetrahydrofuran (THF) was passed through asolvent purification system, which includes a column of activatedalumina and a column of molecular sieves operated under a positivepressure of nitrogen gas. Anhydrous methanol, employed to terminateanionic polymerizations, was sparged with dry nitrogen for 30 minutesprior to use to remove dissolved oxygen.

Linear diblock copolymers were synthesized using sequential anionicpolymerization of tBS, end-capping of the PtBS block with DPE,subsequent polymerization of MMA, and finally termination of thepolymerization using deoxygenated anhydrous methanol. Polymerizationswere performed on a scale of ˜20 grams (g) total monomer and 200 to 250milliliters (mL) of THF solvent in a 1 liter (L) glass pressure reactionvessel containing five threaded ports. To three of the ports wereattached PTFE stoppered flasks containing purified THF, tBS, and MMA allunder argon. To the fourth port was attached a transfer/injection armcapable of varying the atmosphere within the vessel from high-vacuum(about 25 millitorr) to 5 pounds per square inch (psi) (0.35 kilogramsper square centimeter) of dry argon through Cajon tube attachment to amanifold. This arm also contained two other inlets—one hosting a sealedseptum for syringe injection of reagents and the other attached to apressure gauge for monitoring pressure. The fifth port was plugged witha threaded polytetrafluoroethylene stopper. The assembled anionicreaction vessel was evacuated with high-vacuum of 25 mtorr andexcessively flame dried followed by repetitious backfilling with argon,re-evacuating, and flame drying again. After the vessel was sufficientlydry and degassed, a dynamic pressure of 5 psi (0.35 kilograms per squarecentimeter) argon was then applied.

The temperature of the reaction was maintained at −78° C. throughout thepolymerization through use of a dry ice/acetone bath. A representativepolymerization procedure is as follows: After adequate preparation ofthe polymerization vessel described above, the stopper on the THFsolvent flask was opened and about 200 mL was added to the flask andstirred using an egg-shaped polytetrafluoroethylene covered stirringmagnet and a stir plate. The THF was then cooled to −78° C. Once cool, apredetermined amount of sec-butyllithium suitable for the desiredmolecular weight of the target polymer was injected into the cold THFusing an air-tight syringe through the injection port arm on the vessel.

After stirring for 15 minutes, 8.998 g (56.1 mmol) of tBS monomer wasthen slowly added to the reaction vessel. After full monomer addition,the solution was allowed to stir at −78° C. for 1 hour. DPE,approximately 1.5 times the moles of sec-butyllithium initiator used,was then injected into the vessel through the injection septum and thepolymerization solution turned from an orange to a deep red color.

Administering an excess of DPE ensures that all of the chains becomecapped. Only one unit of DPE is capable of addition as it cannotpropagate due to steric restrictions. Following 15 minutes of stirring,a 1 to 2 mL aliquot was removed from the vessel using a long needlesyringe and injected into ˜15 to 20 mL of deoxygenated methanol toterminate and precipitate a small sample of the DPE capped PtBShomopolymer for characterization. Finally, to the bulk reaction, the MMA11.386 g (113.7 mmol) was added slowly and anionic solution immediatelybecame colorless. The MMA addition was allowed to stir for 1 hour. Thepolymerization was terminated with a 1-2 mL injection of degassedmethanol. The vessel was depressurized, warmed to room temperature,disassembled, and the contents poured through a long stemmed funnel intoa stirring solution of methanol (2 L, approximately 10 times the volumeof the THF used). Precipitation of the white polymer occurred and wasfiltered, collected, and air dried to remove a majority of the methanol.It was then dissolved in 200 to 300 mL of THF. The precipitation andfiltration procedure was then repeated. A final drying of the polymer at40° C. in a vacuum oven for 3 days was then performed prior to furtheranalysis. Greater than 97% polymer yield was recovered in all cases.

Dispersities (D) were determined by size exclusion chromatography (SEC)using HP 1100 series components, three successive Varian PLgel Mixed-Ccolumns with chloroform as the mobile phase (at 35° C. and a flow rateof 1 mL/min) and eluents monitored using an HP 1047A RI detector. Valueswere determined based on a ten-point calibration curve using polystyrenestandards purchased from Polymer Laboratories.

Weight average molecular weights (Mw) were determined using a separategel permeation chromatography (GPC) instrument using THF as the mobilephase at a flow of 1 mL/min. The GPC is equipped with a Wyatt TechnologyDAWN DSP multi-angle laser light scattering (MALLS) detector in additionto a Wyatt Optilab EX RI detector. Size exclusion was performed with 3successive Phenomenex Phenogel-5 columns and Mw values were determinedfrom the dn/dc value of PtBS (0.129 mL/g) homopolymer reported in theliterature. The volume fractions (f) of each block was calculated fromthe molar block fractions determined by ¹H-NMR in CDCl₃ on a VarianInova 500 MHz spectrometer with chemical shifts referenced fromtetramethylsilane at 0.00 ppm. Molar fractions were obtained fromintegration comparison of the PtBS aryl protons versus the PMMA methoxyprotons.

Glass transition temperatures (Tg) were determined using differentialscanning calorimetry (DSC) on a TA Instruments Discovery DSC usingT-zero aluminum pans. All BCP samples were heated to 220° C. at 20°C./min, cooled to 0° C. at 20° C./minute, then Tg was determined uponsecond heating at 20° C./minute. Thermogravimetric analysis (TGA) wasperformed on a Perkin Elmer Diamond TG/DTA under nitrogen atmosphere ata heating rate of 10° C./minute.

D-spacing values were obtained from SAXS analysis at 25° C. performed atthe Advanced Photon Source (APS) at Argonne National Laboratory inSector 5-ID-D beamline. The source produces X-rays with a wavelength of0.73 Å.

Scattering intensities were monitored by a Mar 165 mm diameter CCDdetector with a resolution of 2048×2048. Variable temperature (VT)-SAXSanalysis was performed on a 2 meter instrument fitted with a BrukerHi-Star multi-wire area detector, a Rigaku Ultrex 18 kilowatt (kW)generator with copper kα radiation x-rays of monochromaticwavelength=1.54 Å, and a thermally controlled sample chamber capable ofaccessing temperatures between 25 and 200° C. with direct thermocoupleattachment to the sample stage.

The resulting properties for the PtBS-b-PMMA block copolymers aredetailed in Table 1. Calculation of the total degree of polymerization(N) was performed using the density values of PtBS (0.95 g/cm³) and PMMA(1.18 g/cm³) at 298° K and a reference volume, ν₀, of 118 Å³. For eachblock copolymer, the Mw of the PtBS block was determined from thehomopolymer aliquot taken in-situ using MALLS-GPC and converted to M_(n)using the dispersity,

. The total block copolymer M_(n) was then determined from the molarratio by 1H-NMR analysis. For all of the block copolymers, thecomposition (volume fraction fPtBS) lies between 0.50 and 0.55 with

being less than or equal to about 1.20. Thermal stability of PtBS-b-PMMAwas tested by TGA under N₂ with heating from 30 to 600° C. at 10° C./min(FIG. 2). These materials demonstrate stability up to 325° C. and lessthan 5% weight loss up to 350° C. DSC reveals the T_(g) for both blocksoverlap within the range of 125 to 145° C. (FIG. 3). Although only oneglass transition is observed at lower N values, two transitions areapparent at the higher molecular weights.

TABLE 1 Sample Block Mn D T_(ODT) # Copolymer^(a) (kg/mol)^(b) PDI^(c)f_(PtBS) ^(d) N^(e) (nm)^(f) (° C.) 1 PtBS-PMMA 12.5 1.16 0.55 16812.1^(g) (12.5, 0.55) 2 PtBS-PMMA 14.3 1.14 0.53 191 12.4^(g) (14.3,0.53) 3 PtBS-PMMA 17.6 1.18 0.53 236 14.4 192 (17.6, 0.53) 4 PtBS-PMMA19.6 1.15 0.55 263 15.3 215 (19.6, 0.55) 5 PtBS-PMMA 20.5 1.20 0.50 27315.9 228 (20.5, 0.50) 6 PtBS-PMMA 31.1 1.13 0.54 411 19.4 318 (31.1,0.54) 7 PtBS-PMMA 41.6 1.18 0.53 557 24.6 (41.6, 0.53) ^(a)PtBS-PMMA(Y,Z) = PtBS-b-PMMA with a total molecular weight of Y (kg/mole) and avolume fraction of the PtBS block Z. ^(b)Determined using multi-anglelaser light scattering gel permeation chromatography (MALLS-GPC) of PtBShomopolymer and ¹H-NMR molar ratio of each block. ^(c)Dispersitydetermined through SEC analysis. ^(d)PtBS volume fraction determinedusing the 25° C. densities ρ(PtBS) = 0.94 g/cm³ and ρ(PMMA) = 1.18g/cm³. ^(e)Total degree of polymerization based on 118 Å³ referencevolume (í0) . ^(f)Determined using 25° C. SAXS principle lamellarscattering peak q*, where D =2π/q*. ^(g)Denotes disordered morphology.

The data in Table 1 shows that for Sample #s 1 and 2 that have molecularweights of the blocks below 15 kilograms per mole, the samples havedisordered morphologies. At molecular weights greater than 15 kilogramsper mole, the block copolymer has an ordered structure withlamellae/cylinders. When cast as a thin film on a substrate, theselamella/cylinders are periodic and are perpendicular to the surface ofthe substrate. These samples can therefore be used for advancedsemiconductor patterning.

The FIG. 2 is a graph depicting thermal decomposition data of Sample #4obtained using thermogravimetric analysis (TGA). The heating in the TGAwas conducted under nitrogen at a heating rate of 10° C./minute. TGAthermograms shown in the FIG. 2 show that the samples have adecomposition temperature of approximately 350° C., while the graph(inset) shows that the weight loss was less than 5 wt % prior to 350° C.

The FIG. 3 is a graph depicting differential scanning calorimetry (DSC)thermograms for all of the compositions shown in the Table 1. The DSCtraces were obtained at a heating rate of 20° C./minute. The FIG. 3 thatthe samples display a glass transition temperature for both blocksbetween 125 and 145° C. The glass transition temperature for bothindividual blocks overlap, however, two phase transitions can beseparately resolved as the value of N exceeds 400.

SAXS results obtained at 25° C. are presented in the FIG. 4. The domainspacing D=2π/q*, was determined for each specimen, where q* is theposition of the principle (first-order) SAXS peak. Lower M_(n) sampleswere prepared by annealing the bulk block copolymer under vacuum at 190°C. for 4 days. The two highest M_(n) block copolymers were shear alignedthrough the use of a channel die in a melt press at 190° C. Althoughsample temperature during SAXS analysis was 25° C., it is believed thatthe observed pitch of the microdomains are close to those at 190° C. dueto rapid cooling and vitrification of the samples after annealing.

The location of the higher order scattering peaks, with respect to q*,match those calculated (black triangles) for an anticipated lamellarmorphology. The observation of a single broad principle peak forPtBS-PMMA (12.5,0.55) and PtBS-PMMA (14.3, 0.53) suggests the materialsare disordered at 190° C. An ordered lamellar morphology for PtBS-b-PMMA(17.6, 0.53) is indicative of a larger χ when compared to symmetricpolystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymers,where M_(n) at 30 kg/mole is required to obtain microphase separation ata comparable temperature. The secondary scattering peak located at 2q*is barely visible, consistent with the extinction condition for lamellarmorphologies containing nearly equal volumes of each block.

EXAMPLE 2

This example demonstrates the difference between a block copolymercomprising polystyrene and polymethylmethacrylate (PS-b-PMMA) and ablock copolymer comprising poly(4-tert-butyl-styrene) andpolymethylmethacrylate (PtBS-b-PMMA). It also demonstrates theadvantages of the block copolymer comprising poly(4-tert-butyl-styrene)and polymethylmethacrylate over a block copolymer comprising polystyreneand polymethylmethacrylate (PS-b-PMMA).

Current multiple patterning techniques can be used to form line/spacepatterns down to 20 nm pitch, but no practical method exists to formthese patterns at a sub-20 nm pitch. PS-PMMA has been demonstrated toform these patterns at pitch down to 25 nm, but due to its relativelylow χ, PS-PMMA will not self assemble at a pitch below 21 nm. Asdemonstrated by the data, PtBS-PMMA can form self assembled structuresas small as 14 nm and thus solves one important commercial issue withPS-PMMA in that it is extendable to small pitch where industry iscurrently desirous of a solution.

The block copolymer morphology is formed in part by the thermodynamicdrive for the system to minimize interfacial area. A defect results inincreased interfacial area. When χ is higher, the drive to minimizeinterfacial area is stronger, therefore the drive to eliminate defectsis also higher, i.e., higher χ gives fewer defects at equilibrium.

At a given pitch, if a material has a higher χN, many other featuresrelated to the pattern will also be improved, including line-edgeroughness. Below is a comparison of the interfacial width and line-edgeroughness for PS-PMMA and PtBS=PMMA at 25 nm pitch. The relevant numberssuch as periodicity are much lower for PtBS-PMMA (when compared withPS-b-PMMA) due to the higher χ.

Some reports indicate that the self-assembly process can improve linewidth variations and line edge roughness (LER). However, theoretical andexperimental evidence suggests that the inherent line-edge roughness ofPS-PMMA block copolymer systems is not acceptable for semiconductormanufacturing at the 23 nm node. In this analysis, the LER wasdetermined using transmission soft X-ray diffraction (SoXRD) from aline/space pattern formed by PS-PMMA and compared to predicted values ofinterfacial width and the interfacial variance.

The magnitude of the interfacial width, Δ, was calculated as follows:

${\Delta = {\Delta_{0}\lbrack {1 + \frac{1.34}{\chi \; N^{1/3}}} \rbrack}},{\Delta_{0} = {2\; a_{x}{\chi^{- 0.5}/\sqrt{6}}}}$

where N is the total degree of polymerization, χ is the Floryinteraction parameter, and a_(x) is the statistical segment length.Variance in position of the interface

δ_(x) ²

was also calculated as follows:

$\delta_{x}^{2} = {\frac{v\; 6^{1/2}}{2\; \pi \; a_{x}\chi^{0.5}}{\ln ( \frac{d}{\Delta} )}}$

where ν is the monomer volume and d is the lamellar spacing or pitch(also termed periodicity). Accounting for the fluctuation-broadenedinterface, an apparent interfacial width, Δ_(a), can also be determinedaccording to the equation:

Δ_(a) ²=Δ²+2π

δ_(x) ²

From these equations, these parameters can be compared for PS-b-PMMA andPtBS-b-PMMA. For PS-b-PMMA with d=25 nm, the interfacial width can beestimated to be Δ≈4.2 nm, while the variance in the interface positionis predicted to be

δ_(x) ²

≈0.9 nm². These values can be combined to give an apparent interfacialwidth of Δ_(a)≈4.9 nm. In contrast, at d=25 nm, PtBS-b-PMMA is predictedto have a much narrower interfacial width (Δ≈1.6 nm) and variance ininterfacial position (

δ_(x) ²

≈0.6), giving an apparent interfacial width Δ_(a) of only 2.6 nm. Thefollowing physical parameters were used for these calculations:PS-b-PMMA: Mn=42.4 kg/mol, χ=0.037 (at 240° C.), a=0.54 nm,characteristic ratio (C_(∞))=9.3, density (ρ)=0.962 g/cc, ν=0.118 nm³and N=620; PtBS-b-PMMA: Mn=41.6 kg/mol, χ=0.128 (at 240° C.), a=0.59 nm,C_(∞)=10.3, ρ=1.051 g/cc, ν=0.118 nm³, and N=557.

This information shows that because of a larger chi parameter forPtBS-b-PMMA copolymers, the periodicity can be reduced to less than orequal to about 20 nanometers, specifically to less than or equal toabout 15 nanometers. This is not achievable with PS-b-PMMA blockcopolymers. The larger chi parameter for PtBS-b-PMMA copolymers comparedto PS-b-PMMA also leads to materials with sharper block interfaces (i.e.smaller interfacial widths) and lower line edge roughness.

From the aforementioned data it may be seen that when the chi parameter(χ) is greater than or equal to about 0.05, specifically greater than orequal to about 0.075, specifically greater than or equal to about 0.1,and more specifically greater than or equal to about 0.12, the resultingblock copolymer may have lamellar or cylindrical interdomain spacings(i.e., a periodicity) of less than or equal to about 25 nanometers, andspecifically less than or equal to about 20 nanometers.

What is claimed is:
 1. A method comprising: polymerizing a vinylaromatic monomer to form a first block; and polymerizing a second blockonto the first block to form a block copolymer; where the second blockis derived by polymerizing an acrylate monomer; and where the blockcopolymer has a chi parameter of greater than or equal to about 0.05,when measured at 240° C.; where the chi parameter is a measure ofinteractions between the first block and the second block of thecopolymer.
 2. The method of claim 1, where the first block isanionically polymerized and/or the second block is anionicallypolymerized.
 3. The method of claim 1, where the second block issequentially polymerized onto the first block; the sequentialpolymerization comprising polymerizing the acrylate monomer in thepresence of the first block in a single reaction vessel.
 4. The methodof claim 3, where the first block and the second block are polymerizedusing a same initiator.
 5. The method of claim 1, where the vinylaromatic monomer is an alkylstyrene.
 6. The method of claim 1, where thealkylstyrene is o-methylstyrene, p-methylstyrene, m-methylstyrene,α-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene,α-methyl-p-methylstyrene, 2,4-dimethylstyrene, monochlorostyrene,p-tert-butylstyrene, 4-tert-butylstyrene, or a combination comprising atleast one of the foregoing alkylstyrenes.
 7. The method of claim 1,where the acrylate monomer has a structure represented by formula (1):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms. 8.The method of claim 1, where the acrylate monomer has a structurerepresented by the formula (2):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms andR₂ is a C₁₋₁₀ alkyl, a C₃₋₁₀ cycloalkyl, or a C₇₋₁₀ aralkyl group. 9.The method of claim 1, where the acrylate monomer has a structure thatcomprises at least one fluorine atom substituent, where the structurerepresented by the formula (3):

where R₁ is a hydrogen or an alkyl group having 1 to 10 carbon atoms andR₃ is a C₂₋₁₀ fluoroalkyl group.
 10. The method of claim 1, where thefirst block is poly(4-tert-butylstyrene).
 11. The method of claim 1,where the acrylate monomer is a methacrylate, an ethacrylate, a propylacrylate, a methyl methacrylate, a methyl ethylacrylate, a methylpropylacrylate, an ethyl ethylacrylate, a methyl arylacrylate, atrifluoroethyl methacrylate, a dodecafluoroheptylmethacrylate, or acombination comprising at least one of the foregoing acrylate monomers.12. The method of claim 1, where the second block ispolymethylmethacrylate.
 13. The method of claim 1, where the blockcopolymer comprises cylindrical and/or lamellar domains and has aninterdomain spacing of less than or equal to about 25 nanometers.